You can just dismiss you pet during the MC phase. It is very little hp you have to burn through to get him to last phase. When I kill him with my hunter I just move the pet behind the pillar out of habit, but it is a little more complicated and can get buggy.

If you have decent gear though just blow all cooldowns and he won't even have time to cast MC.

Last time i did Kaelthas as a Frostmage (also has pet) was at the beginning of T14 content with a Itemlevel of something like 470 and i just nuked him before he did anything. So unless you have really bad gear it shouldnt be a problem for a hunter too.

If you dont have enough DPS just dismiss your pet after a few seconds in Phase 4 (the one with Mindcontrol).

MC isn't random - it does have a cooldown, but he doesn't use it on-cooldown. Once he uses it, you have 20-30 seconds guaranteed safe time (best to stay on the lower end). Even after that time he may not use it for a bit. I still stand behind the statue out of habit in P4 from doing it at 85 even though I'm sure it's 100% unnecessary nowadays. Or actually, I don't do the fight at all anymore since I finally got my Ashes on my 68th kill.

1. go boss chamber and start the encounter
2. run away close to the entrace of the raid
3. wait for the first assistant of KT to come and kill him
4. wait till the next assistant come
5. proceed to the entrace of the hallway leading to boss chamber and wait for third assistant and kill her
6. get to the entrace of the boss chamber and wait for fourth assistant come and kill him

After that, just take all of them one by one so they cant stack their CC on you. After killing all assistants and their weapons, wait for KT to come out of boss chamber and kill him.

1. go boss chamber and start the encounter
2. run away close to the entrace of the raid
3. wait for the first assistant of KT to come and kill him
4. wait till the next assistant come
5. proceed to the entrace of the hallway leading to boss chamber and wait for third assistant and kill her
6. get to the entrace of the boss chamber and wait for fourth assistant come and kill him

After that, just take all of them one by one so they cant stack their CC on you. After killing all assistants and their weapons, wait for KT to come out of boss chamber and kill him.

Waaaaaaaaaaaaaaaaaaaay more work than is needed at 90. You're just wasting time. In P1, just 2-shot them where they stand. In the 4 advisor phase, just deterrence immediately before they stand up to block Telonicus's remote toy, put pet on him and blow him up. Then kill capernian or sanguinar, and then thaladred. But even if you do it wrong, your risk of dying is next to nothing. Especially if you have spirit bond. With spirit bond you could probably just stand there afk and never die. Only reason I bothered to block Remote Toy is because it's annoying as shit, but it's not a death sentence.